Since it's running on the same chip as the micro:bit, is it safe to assume that if I were to get a programmer and connect it, I could potentially run espruino on this thing? I looked on the forums, and it appears that no one has brought this up before, or my search skills are lacking.

If so, that would be incredible, but I have no idea where to start. I've already mangled this beacon a bit, so if I damage it in the process, it'll be no big loss.

I'm already started on integrating my puck into my home automation system, which will perform context-aware actions based on what room it's in when the button is pressed (and potentially more complex actions based on sensor data). If it can be ported to run on this cheap a device, I can imagine having a set of various beacons attached to devices that would trigger specific actions in certain places (like a beacon that turns on the lights in whatever room you're in when you press it, or a beacon that controls my music system and sets it to the room I'm in).

if I were to get a programmer and connect it, I could potentially run espruino on this thing?

Yes, absolutely. There's an image for NRF51TAG (you'd have to follow the build instructions at https://github.com/espruino/Espruino to build it), but that may just run as-is. Otherwise you may have to tweak the pin assignments in NRF51TAG.py to match your tag.

Realistically the best way to program these is to use an nRF52832DK board and then connect GND, SWD and SWCLK. The DK is £30 or so so does put a bit of a dent in the cost savings of a cheap beacon though :)

However there's a whole new breed of nRF52 trackers and beacons out there that I'd recommend. You get 4x more RAM which really helps (because of fixed overheads that actually means 10x more JS code space).